The present invention relates to a shadow mask for a cathode ray tube (CRT) and, more particularly, to a shadow mask that is adapted for use in a large-sized flat panel CRT.
Generally, in a CRT application, a shadow mask is mounted within a faceplate panel with an inner phosphor screen so that the shadow mask faces the inner phosphor screen at a close distance. The shadow mask has a plurality of beam-guide apertures that ensure that each of R, G and B electron beams strikes only its intended phosphor on the phosphor screen.
The shadow mask has an overall shape corresponding to that of the internal surface of the faceplate panel with the phosphor screen. Recently, as large-sized flat panel CRTs have been the choice of consumers, shadow masks have become flat in accordance with the flat shape of the CRT panel. However, the flat-shaped shadow mask exhibits poor performance characteristics in a CRT application.
For instance, the shadow mask having a radius of curvature of 1.6R or more exhibits weakness in intensity so that it is liable to suffer deformation at external shocks. Such a deformation of the shadow mask causes serious device failure.
Furthermore, a flat-shaped shadow mask involves a serious doming phenomenon. It is well known that 70% or more of the electron beams emitted from the electron gun do not pass through beam-guide apertures of the shadow mask, and strike the non-aperture portions of the shadow mask. The electron beams striking the shadow mask induce thermal transformation of the shadow mask so that the beam-guide apertures of the shadow mask deviate from their proper positions and the electron beams leaving the shadow mask cannot correctly land in the proper position on the phosphor screen. The doming phenomenon becomes particularly serious when the shadow mask becomes flat, resulting in poor color purity.
The flat-shaped shadow mask further involves a serious howling phenomenon. The flat-shaped shadow mask is liable to vibrate due to external factors such as a sound pressure from the speaker. This howling phenomenon also becomes particularly serious when the shadow mask becomes flat, resulting in poor display image.
It is an object of the present invention to provide a shadow mask that can be well adapted to use in a large-sized flat panel CRT.
This and other objects may be achieved by a shadow mask including a beam-guide member having a substantially rectangular shape with opposite sides in a first axis direction and opposite sides in a second axis direction, the sides in the first axis direction being shorter than those in the second axis direction. The beam-guide member is provided with a plurality of apertures and tie bars interconnecting the neighboring apertures in the first and second axis directions. Each aperture has an opening portion and a tapering portion surrounding the opening portion. A skirt with a bent end portion is extended from the beam-guide member.
The beam-guide member is structured such that the relation of a length A of the tie bar in the first axis direction to a pitch Pv between the neighboring apertures in the first axis direction satisfies the following condition: 0.05xe2x89xa6A/Pvxe2x89xa60.15. The pitch Pv is established to be in the range of 0.6 mm to about 1.0 mm, and the length A of the tie bar is established to be in the range of 0.05 mm to about 0.09 mm. The relation of the length A of the tie bar to a distance B between adjacent end lines of the opening portions of the neighboring apertures in the first axis direction satisfies the following condition: 0.185xe2x89xa6A/Bxe2x89xa60.818. The distance B between the adjacent end lines of the opening portions of the neighboring apertures in the first axis direction is established to be in the range of 0.11 mm to about 0.27 mm. A radius of curvature RS of the shadow mask satisfies the following condition: 1.6Rxe2x89xa6RSxe2x89xa64R where 1R indicates a diagonal length of an effective screen area of the panel multiplied by 1.767.
Alternatively, the shadow mask may have varying curvature radii R1 and R2 in different areas. In this case, the curvature radius R1 at the two third horizontal area of the beam-guide member on the basis of a central axis of the beam-guide member, and the curvature radius R2 at the remaining one third horizontal area of the beam-guide member satisfy the following condition: R2xc3x971.5xe2x89xa6R1xe2x89xa6R2xc3x975.